Introduction to the CohortThe Origins of Variance in the Oldest-Old (OCTO-TWIN) study is a longitudinal study of twin-pairs drawn from the Swedish Twin Registry (STR). The study aimed to investigate the etiology of individual differences among this subset of the “oldest-old” on a range of domains including health and functional capacity, cognitive functioning, psychological well-being, personality and personal control, and interpersonal functioning.

OCTO-TWIN began in 1991 and included all twins from the STR who were at least 80 years old during the baseline period (1991-1994) who agreed to participate. At baseline, 351 twin-pairs (702 individuals) were available. Twin pairs were followed until 1999. There were three follow-up visits, each approximately 2 years apart during this period.

As all individuals in OCTO-TWIN are part of the STR, information regarding health-related behaviors such as smoking, diet, physical activity, personality and exposure to environmental stressors will be available for some individuals from earlier STR questionnaires sent to members in 1961, 1963, 1967, 1970 and 1973. Questionnaires were also sent to cohort members over the course of the study.

Ethnicity BreakdownAll participants were born in Sweden. While this study did not specifically report any information on ethnicity, another study that used a cohort made up of subsamples from the Swedish Twin Registry has described the OCTO-TWIN participants as Caucasian (Jansson et al., 2003).